The invention relates to methods and apparatus for metal casting, and more particularly to methods and apparatus for casting an air cooled cylinder head in a lost foam casting process. Even more particularly, the invention relates to foam patterns and methods for making foam patterns for casting an air cooled cylinder head in a lost foam casting process.
A foam mold pattern for use in a lost foam casting process is commonly formed by injecting polystyrene beads into a mold having a cavity with the shape of the desired foam pattern. While the polystyrene beads can theoretically have any size, the most readily available and by far most economical size is that used in forming styrofoam cups. Smaller beads are much more expensive, or even unobtainable. When using conventional methods, it is difficult if not impossible to obtain satisfactory "fill out" of a foam pattern, or of the passages of a mold cavity used in forming a foam pattern, if any portion of the foam pattern having a significant length (one inch, for example) has a thickness of less than three to four times the diameter of the beads being used to form the pattern. When using conventionally sized beads, it is difficult to fill out pattern portions having a thickness of less than 0.180 inches
A thickness of 0.180 inches is too thick for effective cooling fins on an air cooled cylinder head. Thus, a foam pattern for an air cooled cylinder head with satisfactorily thin cooling fins cannot be formed by molding the pattern in one piece, because the "fins" of the pattern will not satisfactorily fill out.
It is known in the lost foam casting art to form a foam pattern by gluing various pieces of a pattern together.
Attention is directed to the following United States patents which relate to casting with evaporative patterns and to casting of engine parts:
______________________________________ Ernest 4,197,899 April 15, 1980 Erdle 2,461,416 February 8, 1949 Wittmoser 3,302,256 February 7, 1967 Boyle 3,898,654 November 19, 1974 Witchell 4,015,654 April 5, 1977 Bretzger 4,231,413 November 4, 1980 Trumbauer Re.31,488 January 10, 1984 Trumbauer 4,462,453 July 31, 1984 ______________________________________